i30 



MODIFIED CIKCUMNUXATION. 



Chap. VIII 



Fig. 176. 



10.40 P.M., -when the last dot was made. Here, then, we have 

 a distinct heliotropio movement, effected by means of six 

 elongated figures (which if dots had been made every few 

 minutes would have been more or less elliptic) directed towards 

 the Mght, with the apex of each suc- 

 cessive ellipse nearer to the window 

 than the previous one. Now, if the 

 light had been only a little brighter, 

 tbe epicotyl would have bowed itself 

 more to the light, as we may safely 

 conclude from the previous trials ; 

 there would also have been less 

 lateral movement, and the ellipses or 

 other figures would have been drawn 

 out into a strongly marked zigzag 

 line, with probably one or two small 

 loops still formed. If the light had 

 been much brighter, we should have 

 had a slightly zigzag line, or one 

 quite straight, for there would have 

 been more movement in the direc- 

 tion of the light, and much less from 

 side to side. 



Sachs states that the older inter- 

 nodes of this Tropseolum are aphe- 

 liotopic; we therefore placed a 

 plant. 111 inches high, in a box, 

 blackened Avithin, but open on one 

 side in front of a north-east window 

 without any blind. A filament was 

 fixed to the third internode from 

 the summit on one plant, and to 

 the fourth internode of another. 

 These internodes were either not 

 old enough, or the light was not suf- 

 ficiently bright, to induce aphelio- 

 tropism, for both plants bent slowly towards, instead of from 

 the window during four days. The course, during two days of 

 the first-mentioned internode, is given in Tig. 176 ; and we see 

 that it either oircumnutated on a small scale, or travelled in a 

 zigzag line towards the light. "We have thought this case of 

 feeble heliotropism in one of the older internodes of a plant, 



TropiBolum majus: heliotropic 

 movement and circumnuta- 

 tion of an old internode to- 

 wards a lateral light, traced 

 on a horizontal glass from 8 

 A.M. Not. 2nd to 10 20 A.M. 

 Nor. 4th. Broken lines show 

 the nocturnal course. 



